Various types of proportional control valves exist which use multiple valves which are electromagnetically actuated. Examples of such are described in U.S. Pat. No. 3,893,471 issued to Byers, Jr.; and U.S. Pat. No. 4,300,873 issued to Mowbray et al. In these types of proportional control valves, the force which can be developed by a given size solenoid is inversely proportional to the air gap across which the magnetic flux must jump for any given current. The prior art valves have modified the magnetic characteristics to obtain a constant force over a wide air gap thereby producing a linear relationship between input current and valve stroke. By doing so, the effect of the air gap is minimized and the maximum useable force level is sacrificed. This means that the valve stroke and thus the flow capacity of the valve can only be increased by increasing the power input to the valve, which is not feasible in many instances.
Now, a proportional control valve has been invented which utilizes an essentially constant and small air gap across which a magnetic flux crosses such that an increased force is obtainable there increasing the length of stroke of the valve.